In cells infected with small DNA tumor viruses, the onset of apoptosis is triggered by the induction of unscheduled cellular DNA synthesis by viral early proteins. In cells infected with human adenoviruses (Adv), the proteins coded by the early region E1A play a central role in inducing apoptosis and the process is actively suppressed by E1B-19K which is a viral homolog of BCL-2. Studies on Adv- induced apoptosis have served as the model for apoptosis induced by other viral infections. Adv also serves as a valuable tool to dissect the normal and pathological functions of apoptosis regulators. During Adv-induced apoptosis, the BH3-only protein BIK functions as the apical effector. BIK-mediated apoptosis signaling results in the activation of multi-domain (BH1-3) pro-apoptotic members BAX and BAK. The present renewal application will focus on unraveling the functions of two E1B-19K target BH3-only molecules BIK and BNIP3, and the BH1-3 molecules BAK and BAX in virus-induced apoptosis and apoptotic injury in an animal model and in cancer development. In Aim 1, we will investigate the mode of transcriptional activation of Bik through an E2F-1 dependent pathway, a novel post- transcriptional mode of activation of BIK by viral oncogenes that interact with pRB. The role of virus- induced apoptosis in Adv-induced apoptotic liver damage will be investigated in the Bik-null mouse model. We will also use an immunodeficient mouse model to evaluate anti-apoptosis therapeutics to inhibit virus-induced hepatic injury. We have postulated that viruses may exploit apoptosis for intercellular spread during late stages of viral infection. Our results suggest that BAX and BAK may have novel functions in viral egress and spread. In Aim 2, we will use Adv to elucidate novel functions of BAX and BAK by which they promote or restrict viral spread. Clinical results and experimental evidence suggest that the E1B-19K target molecule BNIP3 plays a fundamental role in the development of solid tumors such as lung and breast carcinomas. In Aim 3, we will investigate the role of BNIP3 in tumor development and progression using Bnip3 knockout mouse and a conditional p53-Rb1 KO lung cancer mouse model. In this Aim, we will also investigate the roles of BNIP3 in regulating Adv-induced autophagy and autophagic cell death. Our proposed studies on these critical cellular apoptosis regulators may provide important new insights on their role in virus-induced apoptosis, viral spread and pathogenesis. These results will have broad relevance to other virus and pathogen infections. The proposed studies on the E1B-19K target molecules BNIP3 and BIK may illuminate their roles in the development and progression of lung, breast and colon cancers and may suggest strategies to inhibit tumorigenesis and tumor progression.